Coordinated dimmer compatibility functions

ABSTRACT

A system and method includes a controller that is configured to coordinate (i) a low impedance path for a dimmer current, (ii), control of switch mode power conversion and (iii) an inactive state to, for example, to allow a dimmer to function normally from cycle to cycle of an alternating current (AC) supply voltage. In at least one embodiment, the dimmer functions normally when the dimmer conducts at a correct phase angle indicated by a dimmer input setting and avoids prematurely resetting while conducting. In at least one embodiment, by coordinating functions (i), (ii), and (iii), the controller controls a power converter system that is compatible with a triac-based dimmer. In at least one embodiment, the controller coordinates functions (i), (ii), and (iii) in response to a particular dimming level indicated by a phase cut, rectified input voltage supplied to the power converter system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) and 37C.F.R. §1.78 of U.S. Provisional Application No. 61/369,202, filed Jul.30, 2010, and entitled “LED Lighting Methods and Apparatuses” and isincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of electronics,and more specifically to a method and system for coordinating dimmercompatibility functions.

2. Description of the Related Art

Electronic systems utilize dimmers to modify output power delivered to aload. For example, in a lighting system, dimmers provide an input signalto a lighting system, and the load includes one or more light sourcessuch as one or more light emitting diodes (LEDs) or one or morefluorescent light sources. Dimmers can also be used to modify powerdelivered to other types of loads, such as one or more motors or one ormore portable power sources. The input signal represents a dimming levelthat causes the lighting system to adjust power delivered to a lamp,and, thus, depending on the dimming level, increase or decrease thebrightness of the lamp. Many different types of dimmers exist. Ingeneral, dimmers use a digital or analog coded dimming signal thatindicates a desired dimming level. For example, some analog baseddimmers utilize a triode for alternating current (“triac”) device tomodulate a phase angle of each cycle of an alternating current (“AC”)supply voltage. “Modulating the phase angle” of the supply voltage isalso commonly referred to as “chopping” or “phase cutting” the supplyvoltage. Phase cutting the supply voltage causes the voltage supplied toa lighting system to rapidly turn “ON” and “OFF” thereby controlling theaverage power delivered to the lighting system.

FIG. 1 depicts a lighting system 100 that includes a leading edge dimmer102. FIG. 2 depicts exemplary voltage graphs 200 associated with thelighting system 100. Referring to FIGS. 1 and 2, the lighting system 100receives an AC supply voltage V_(SUPPLY) from voltage supply 104. Thesupply voltage V_(SUPPLY), indicated by voltage waveform 202, is, forexample, a nominally 60 Hz/110 V line voltage in the United States ofAmerica or a nominally 50 Hz/220 V line voltage in Europe. A leadingedge dimmer phase cuts leading edges, such as leading edges 204 and 206,of each half cycle of supply voltage V_(SUPPLY). Since each half cycleof supply voltage V_(SUPPLY) is 180 degrees of the supply voltageV_(SUPPLY), a leading edge dimmer phase cuts the supply voltageV_(SUPPLY) at an angle greater than 0 degrees and less than 180 degrees.Generally, the voltage phase cutting range of a leading edge dimmer 102is 10 degrees to 170 degrees. The leading edge dimmer 102 can be anytype of leading edge dimmer such as a triac-based leading edge dimmeravailable from Lutron Electronics, Inc. of Coopersberg, Pa. (“Lutron”).A triac-based leading edge dimmer is described in the Background sectionof U.S. patent application Ser. No. 12/858,164, entitled Dimmer OutputEmulation, filed on Aug. 17, 2010, and inventor John L. Melanson.

Ideally, by modulating the phase angle of the dimmer output voltageV_(φ) _(—) _(DIM), the leading edge dimmer 102 effectively turns theconstant current lamp 122 OFF during time period T_(OFF) and ON duringtime period T_(ON) for each half cycle of the supply voltage V_(SUPPLY).Thus, ideally, the dimmer 102 effectively controls the average powersupplied to the constant current lamp 122 in accordance with the dimmeroutput voltage V_(φ) _(—) _(DIM). However, in many circumstances, theleading edge dimmer 102 does not operate ideally. For example, when theconstant current lamp 122 draws a small amount of current i_(DIM), thecurrent i_(DIM) can prematurely drop below a holding current value HCbefore the supply voltage V_(SUPPLY) reaches approximately zero volts.When the current i_(DIM) prematurely drops below the holding currentvalue HC, a triac-based leading edge dimmer 102 prematurely resets, i.e.prematurely disengages (i.e. turns OFF and stops conducting), and thedimmer voltage V_(φ) _(—) _(DIM) will prematurely drop to zero. Anexemplary premature reset would occur if the dimmer 102 reset at time t₃and the dimmer voltage V_(φ) _(—) _(DIM) dropped to 0V at time t₃. Whenthe dimmer voltage V_(φ) _(—) _(DIM) prematurely drops to zero, thedimmer voltage V_(φ) _(—) _(DIM) does not reflect the intended dimmingvalue as set by the resistance value of variable resistor 114. The diodefor alternating current (“diac”) 119, capacitor 118, resistor 116, andvariable resistor 114 form a timing circuit 116 that resets triac 106.Additionally, the triac 106 of leading edge dimmer 102 can reset andthen conduct repeatedly, i.e. disengage (non-conductive), reengage(conductive), disengage (non-conductive), and so on repeatedly during ahalf-cycle of supply voltage V_(SUPPLY) when the current i_(DIM) isbelow or near the holding current value HC. A “reset-conduct” sequenceoccurs when the dimmer 102 resets and then conducts the supply voltageV_(SUPPLY) one or more times during a single half-cycle of the supplyvoltage V_(SUPPLY).

The lighting system 100 includes a resistor, inductor, capacitor (RLC)network 124 to convert the dimmer voltage V_(φ) _(—) _(DIM) to anapproximately constant voltage and, thus, provide an approximatelyconstant current i_(OUT) to the constant current lamp 122 for a givendimmer phase angle. Although relatively simply to implement, the RLCnetwork 124 is inefficient because of, for example, resistor-based powerlosses. Additionally, reactive load presented by the RLC network 124 tothe dimmer 102 can cause the triac to malfunction.

SUMMARY OF THE INVENTION

In at least one embodiment, a dimmer voltage to a power converter systemincludes three states that occur from:

-   -   A. an approximately zero volt crossing of the dimmer voltage of        a dimmer until a phase cut, leading edge of the dimmer voltage;    -   B. an end of state A until energy transferred to a load is        sufficient to meet at least one energy transfer parameter; and    -   C. an end of state B until a beginning of state A.

In one embodiment of the present invention, an apparatus comprises acontroller. The controller is configured to:

-   -   for state A, enable a low impedance path for a dimmer current of        the dimmer, wherein the impedance of the low impedance path is        sufficiently low to maintain a stable phase angle of the dimmer;    -   for state B,        -   enable control of switch mode power conversion of the dimmer            voltage; and        -   control the switch mode power conversion to maintain the            dimmer current above a current threshold; and    -   for state C, enter an inactive state, wherein during the        inactive state the low impedance path and the control of mode        power conversion is disabled.

In another embodiment of the invention, a method includes:

-   -   for state A, enabling a low impedance path for a dimmer current        of the dimmer, wherein the impedance of the low impedance path        is sufficiently low to maintain a stable phase angle of the        dimmer;    -   for state B:        -   enabling control of switch mode power conversion of the            dimmer voltage; and        -   controlling switch mode power conversion to maintain the            dimmer current above a threshold; and    -   for state C, entering an inactive state, wherein during the        inactive state the low impedance path and the control of mode        power conversion is disabled.

In a further embodiment of the present invention, an apparatuscomprises:

-   -   for state A, means for enabling a low impedance path for a        dimmer current of the dimmer, wherein the impedance of the low        impedance path is sufficiently low to maintain a stable phase        angle of the dimmer;    -   for state B:        -   means for enabling control of switch mode power conversion            of the dimmer voltage; and        -   means for controlling switch mode power conversion to            maintain the dimmer current above a threshold; and    -   for state C, means for entering an inactive state, wherein        during the inactive state the low impedance path and the control        of mode power conversion is disabled.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features and advantages made apparent to those skilled in theart by referencing the accompanying drawings. The use of the samereference number throughout the several figures designates a like orsimilar element.

FIG. 1 (labeled prior art) depicts a lighting system that includes aleading edge dimmer.

FIG. 2 (labeled prior art) depicts exemplary voltage graphs associatedwith the lighting system of FIG. 1.

FIG. 3 depicts an electronic system that includes a controller tocontrol a power converter system by coordinating the functions of a gluecircuit, a dimmer emulator, and a switch mode power conversioncontroller.

FIG. 4 depicts an electronic system that represents one embodiment ofthe electronic system of FIG. 3.

FIG. 5 depicts a controller function coordination process for theelectronic system of FIG. 4.

FIG. 6 depicts exemplary signals in the electronic system of FIG. 4 whenutilizing the controller function coordination process of FIG. 5.

FIG. 7 depicts an embodiment of an inactive state controller of theelectronic system of FIG. 4.

DETAILED DESCRIPTION

In at least one embodiment, a system and method includes a controllerthat is configured to coordinate (i) a low impedance path for a dimmercurrent, (ii), control of switch mode power conversion and (iii) aninactive state to, for example, reduce the dimmer current while allowinga dimmer to function normally from cycle to cycle of an alternatingcurrent (AC) supply voltage. In at least one embodiment, the dimmerfunctions normally when the dimmer conducts at a correct phase angleindicated by a dimmer input setting and avoids prematurely resettingwhile conducting. In at least one embodiment, by coordinating functions(i), (ii), and (iii), the controller controls a power converter systemthat is compatible with a triac-based dimmer. In at least oneembodiment, the controller coordinates functions (i), (ii), and (iii) inresponse to a particular dimming level indicated by a phase cut,rectified input voltage supplied to the power converter system. In atleast one embodiment, as the dimming level changes, the controlleradjusts coordination of functions (i), (ii), and (iii) so that the powerconverter system provides a constant current to the load for eachdimming level. In at least one embodiment, the system operating undercontrol of the controller reduces resistor-based power losses whileproviding compatibility between the triac-based dimmer and a loadreceiving a constant current for a dimming level.

In at least one embodiment, a dimmer generates a voltage that isrectified and provided to the power converter system as a dimmer outputvoltage. The dimmer output voltage includes three states. In at leastone embodiment, the three states are sequential and non-overlapping and,i.e. the three states occur one after another and do not overlap intime. In at least one embodiment, the dimmer output voltage to the powerconverter system includes three states that occur from:

-   -   A. an approximately zero volt crossing of the dimmer output        voltage of the dimmer until a phase cut, leading edge of the        dimmer output voltage;    -   B. an end of state A until energy transferred to a load is        sufficient to meet at least one energy transfer parameter; and    -   C. an end of state B until a beginning of state A;

Other embodiments of the dimmer output voltage can have, for example,additional states. The states in A, B, and C can be sub-divided intosub-states.

Given the three foregoing states, in at least one embodiment, thecontroller of the electronic system is configured to coordinatefunctions (i), (ii), and (iii) as follows:

-   for state A, enable a low impedance path for a dimmer current of the    dimmer, wherein the impedance of the low impedance path is    sufficiently low to maintain a stable phase angle of the dimmer;-   for state B, enable control of switch mode power conversion of the    dimmer output voltage, wherein the control of mode power conversion    maintains the dimmer current above a threshold; and-   for state C, enter an inactive state, wherein during the inactive    state the low impedance path and the control of mode power    conversion is disabled.

FIG. 3 depicts an electronic system 300 that includes a controller 302to control power converter system 304 by, for example, coordinating thefunctions of low impedance path state controller 310, and a switch modepower conversion controller 312, and inactive state controller 314 toprovide compatibility between the dimmer 306 and the load 308 so that,for example, the dimmer 306 functions normally. In at least oneembodiment, the power converter system 304 includes a switching powerconverter 318 that converts a dimmer voltage V_(φ) _(—) _(DIM) fromdimmer 306 into a regulated output voltage V_(LINK). The power convertersystem 304 also provides a current i_(OUT) for a load 308. The load 308can be any load including a lamp that includes one or more lightemitting diodes (LEDs). In at least one embodiment, the current i_(OUT)is an approximately constant current for a dimming level of the dimmer306. An “approximately constant current for a dimming level” means thatfor a particular dimming level, the current i_(OUT) will have anapproximately constant value. Dimmer 306 can be any type of dimmer, suchas a triac-based dimmer identical to dimmer 102 of FIG. 1. In at leastone embodiment, dimmer 306 is a “smart dimmer” that includes atriac-based, supply voltage phase cutting circuit. “Smart dimmers” referto a class of dimmers that include a microprocessor to control variousfunctions such as setting the dimmer level.

In at least one embodiment, the controller 302 supports a normaloperation of the dimmer 306 by restraining the dimmer 306 fromprematurely resetting and supporting a stable phase angle cut for agiven dimming level to prevent phase cutting at a wrong phase angle fora set dimming level. In at least one embodiment, the controller 302 alsoprovides a constant output current i_(OUT) corresponding to a dimmerlevel set by dimmer 306. A “wrong” phase angle is, for example, a phaseangle that differs from a phase angle set by the timer 115, which canoccur if, for example, capacitor 121 (FIG. 1) prematurely discharges.For loads, such as one or more light emitting diodes, that utilize asmall output current i_(OUT), especially at low dimming levels, theoutput current i_(OUT) utilized by the loads can be insufficient tosupport a normal operation of a triac-based dimmer 306.

In at least one embodiment, the controller 302 enables the low impedancepath state controller 310 to provide a low impedance current path 316 tothe dimmer 306 from an approximately zero volt crossing of the dimmervoltage V_(φ) _(—) _(DIM) of the dimmer 306 until a phase cut, leadingedge of the dimmer voltage V_(φ) _(—) _(R). As subsequently describedwith reference to FIG. 6, the zero crossing of the dimmer voltage V_(φ)_(—) _(R) occurs at an end of each cycle of the dimmer voltage V_(φ)_(—) _(R) when the dimmer voltage V_(φ) _(—) _(R) approximately reaches0V. In at least one embodiment, the dimmer voltage V_(φ) _(—) _(R)approximately reaches 0V when the dimmer voltage V_(φ) _(—) _(R) has avoltage value less than or equal to 0+ a zero crossing voltage thresholdV_(ZC) _(—) _(TH). The particular value of the zero crossing voltagethreshold is a matter of design choice and, in at least one embodiment,is 5V. The particular impedance value of current path 316 is a matter ofdesign choice. In at least one embodiment, the impedance value ofcurrent path 316 is sufficiently low to allow a sufficient dimmercurrent i_(DIM) to flow through dimmer 306 to provide a stable phaseangle for dimmer 306, i.e. prevent the dimmer 306 from firing at thewrong phase angle. In at least one embodiment, enabling the lowimpedance path 316 at the zero crossing of the dimmer voltage V_(φ) _(—)_(R) supports consistent timing for the phase angle cutting by thedimmer 306 for a given dimming level. Thus, the phase angle cut by thedimmer 306 for a given dimming level remains consistent. In at least oneembodiment, providing the low impedance current path 316 to dimmer 306prevents the dimmer current i_(DIM) from decreasing below a holdingcurrent (HC) value of a triac-based dimmer 306.

At an end of the phase cut of supply voltage V_(SUPPLY), controller 302disables the glue circuit 302, and the glue circuit 302 releases the lowimpedance current path 316, i.e. low impedance current path 316 isdisabled or placed in a high impedance state to substantially preventcurrent flow through current path 316. At the end of the phase cut,controller 302 enables the switch mode power conversion controller, andthe switch mode power conversion controller 312 generates a controlsignal CS to control power conversion by the power converter system 304.In at least one embodiment, the controller 302 senses the link voltageV_(LINK), and, when the link voltage V_(LINK) is greater than a linkvoltage threshold value, the controller 302 disables the switch modepower conversion controller 312. The particular value of the linkvoltage threshold is a matter of design choice. In at least oneembodiment, the link voltage threshold value is set so that the linkvoltage V_(LINK) can be maintained at an approximately DC value. In atleast one embodiment, the switch mode power conversion controller 312maintains the dimmer current i_(DIM) at a level so that the dimmer 306remains in a conductive state from an occurrence of a phase cut, leadingedge of the dimmer voltage V_(φ) _(—) _(R) until energy transferred tothe load 308 is sufficient to meet at least one energy transferparameter, such as the link voltage V_(LINK) is above a target linkvoltage V_(LINK) _(—) _(TARGET) and dimmer 306 has been in a conductivestate until a zero crossing of the supply voltage V_(SUPPLY) so that thedimmer 306 does not prematurely reset. A premature reset can also causeinstability in phase cutting by dimmer 306 and, thus, cause the dimmer306 to cut the supply voltage V_(SUPPLY) at a wrong phase angle.

In at least one embodiment, when the controller 302 disables the switchmode power conversion controller 312, the controller 302 enables theinactive state controller 314. In at least one embodiment, the inactivestate controller 314 causes the dimmer current i_(DIM) to drop toapproximately 0 A and determines a zero crossing of the dimmer voltageV_(φ) _(—) _(R). In at least one embodiment, the inactive statecontroller 314 determines the zero crossing so that the low impedancepath state controller 310 can enable the low impedance path 316 at thezero crossing and support stable phase cutting angles by the dimmer 306so that the dimmer 306 remains stable for a given dimming level. In atleast one embodiment, the inactive state controller 314 generates anemulated dimmer voltage V_(φ) _(—) _(DIM) to, for example, determine azero crossing of the dimmer voltage V_(φ) _(—) _(R). In at least oneembodiment, the inactive state controller 314 generates the emulateddimmer voltage by enabling the current path 316 to discharge a currentthat is inversely proportional to the dimmer voltage V_(φ) _(—) _(DIM).In at least one embodiment, the inactive state controller 314 shapes thedischarged current so that the emulated dimmer voltage approximates anactual dimmer voltage V_(φ) _(—) _(DIM). The term “determine” andderivatives thereof contemplates analytical determination, detection byobservation, or a combination of analytical determination and detectionby observation.

FIG. 4 depicts an electronic system 400, which represents one embodimentof electronic system 300. Electronic system 400 includes controller 402,and controller 402 includes low impedance path state controller 404,switch mode power conversion controller 406, and inactive statecontroller 408. The controller 402 coordinates the low impedance pathstate controller 404, switch mode power conversion controller 406, andinactive state controller 408. Controller 402 represents one embodimentof the controller 302. The low impedance path state controller 404represents one embodiment of the low impedance path state controller310. The switch mode power conversion controller 406 represents oneembodiment of the switch mode power conversion controller 312, and theinactive state controller 408 represents one embodiment of the inactivestate controller 314.

Electronic system 400 includes a power converter system 410 to convertthe dimmer voltage V_(φ) _(—) _(DIM) into a regulated, approximately DCoutput voltage V_(LINK) for load 308. Voltage source 412 supplies analternating current (AC) input voltage V_(SUPPLY) through the seriesconnected, triac-based dimmer 414 to a full bridge diode rectifier 416.In at least one embodiment, dimmer 414 is identical to dimmer 306 (FIG.3). The voltage source 412 is, for example, a public utility, and the ACsupply voltage V_(SUPPLY) is, for example, a 60 Hz/110 V line voltage inthe United States of America or a 50 Hz/220 V line voltage in Europe.The dimmer 414 provides a dimmer voltage V_(DIM). In at least oneembodiment, the dimmer 414 is a leading edge dimmer, and the dimmervoltage V_(φ) _(—) _(DIM) has a leading phase cut when the dimmer 414generates a dimming level between approximately 0 and 100%. The fullbridge rectifier 416 supplies a rectified AC dimmer voltage V_(φ) _(—)_(R) to the power converter system 410. Thus, the dimmer voltage V_(φ)_(—) _(R) represents a rectified version of the dimmer voltage V_(φ)_(—) _(DIM).

Capacitor 418 filters high frequency components from rectified dimmervoltage V_(φ) _(—) _(R), Capacitors 418 and 420 establish a voltagedivider to set a gate bias voltage V_(g) for the source follower fieldeffect transistor (FET) 422. Resistor 407 reduces peak currents throughdiode 426. In at least one embodiment, the particular capacitance valuesof capacitors 418 and 420 are a matter of design choice. In at least oneembodiment, the capacitance of capacitor 418 is 22-47 nF, and thecapacitance of capacitor 420 is 47 nF. Diode 424 prevents the gatecurrent i_(g) from being conducted to the voltage reference V_(REF),such as a ground reference. The gate current i_(g) is conducted throughdiode 426, which prevents reverse current flow of the gate currenti_(g), to the gate of source follower FET 422. Zener diode 428 clampsthe gate of source follower FET 422 to the gate voltage V_(g).

The gate bias voltage V_(g) minus the source voltage V_(S) of FET 422exceeds a threshold voltage of FET 422. During start-up of powerconverter system 410, FET 422 conducts current i_(R) through diode 430to charge capacitor 432 to the operating voltage V_(DD). In at least oneembodiment, after start-up, an auxiliary power supply 434 provides anoperational voltage V_(DD) for controller 402. An exemplary auxiliarypower supply 434 is described in U.S. patent application Ser. No.13/077,421, filed on Mar. 31, 2011, entitled “Multiple Power Sources fora Switching Power Converter Controller”, inventors John L. Melanson andEric J. King, assignee Cirrus Logic, Inc. (referred to herein as“Melanson I”). Melanson I is hereby incorporated by reference in theirentireties.

The capacitance of capacitor 432 is, for example, 10 μF. At start-up,the operating voltage V_(DD) across capacitor 432 equals the Zenervoltage V_(Z) minus the threshold voltage V_(T422) of FET 422 minus thediode voltage V_(d) across diode 430, i.e. at start-upV_(DD)=V_(Z)−V_(T422)−V_(d). FET 422 is a high voltage FET that is alsoused to control boost-type switching power converter 436, and thethreshold voltage V_(T422) of FET 422 is, for example, approximately 3V.

FIG. 5 depicts a controller function coordination process 500 thatrepresents one embodiment of a process used by controller 402 (FIG. 4)to coordinate the functions of the low impedance path state controller404, the switch mode power conversion controller 406, and the inactivestate controller 408 and thereby provide compatibility between dimmer414 and load 308. FIG. 6 depicts exemplary signals and states of thedimmer voltage V_(φ) _(—) _(R) and dimmer current i_(DIM) in theelectronic system 400 when controller 402 utilizes the controllerfunction coordination process 500. In at least one embodiment,controller 402 includes a memory (not shown) that includes code thatimplements one or more operations of controller function coordinationprocess 500. In at least one embodiment, controller 402 also includes aprocessor (not shown) that is connected to the memory and executes thecode and, thus, the operations of the controller function coordinationprocess 500. In at least one embodiment, the controller functioncoordination process 500 is implemented using any combination of analog,digital, analog and digital, and/or microprocessor components. Theparticular implementation is a matter of design choice.

Referring to FIGS. 4, 5, and 6, in at least one embodiment, thecontroller function coordination process 500 initiates at the beginningof state A at an initial zero crossing of the dimmer voltage V_(φ) _(—)_(R). In at least one embodiment, the controller 402 begins operation502 at approximately each zero-crossing of the rectified dimmer voltageV_(φ) _(—) _(R), such as within 0-5V of each zero crossing. Operation502 enables low impedance path state controller 404. When the lowimpedance path state controller 404 is enabled, FET 422 conducts, andthe drain-to-source impedance of FET 422 is very low, e.g. a few ohms.Additionally, the frequency of the rectified input current i_(R) is lowso that the impedance of inductor 438 is low. Thus, the overallimpedance of the low impedance path for current i_(DIM) is a few ohms,such as between 0 and 100 ohms.

In at least one embodiment, for a new cycle of the rectified inputvoltage V_(φ) _(—) _(R), operation 502 begins at the zero crossing 602,which is the beginning of state A. When operation 502 begins, therectified input voltage V_(φ) _(—) _(R) is less than the operatingvoltage V_(DD) plus the forward bias voltage of diode 430. Thus, thediode 430 is reversed biased, and the source voltage V_(S) at sourcenode 407 is approximately equal to the rectified dimmer voltage V_(φ)_(—) _(R) at node 444. The enabled low impedance path state controller404 keeps the source voltage V_(S) at approximately 0V and creates a lowimpedance current path 403 through inductor 438 and FET 422 for therectified input current i_(R) to flow. Thus, the supply currenti_(SUPPLY) is non-zero as indicated by the non-zero dimmer currenti_(DIM) during state A. Thus, the supply current i_(SUPPLY) continues toflow to the dimmer 414 during operation 502 to, in at least oneembodiment, stabilize the cycle-to-cycle phase cutting angle by dimmer414 for a given dimming level.

While the low impedance path state controller 404 is enabled inoperation 502, controller function coordination process 500 performsoperation 506. Operation 506 determines whether the low impedance pathstate controller 404 has detected a leading edge, such as leading edge604, of the rectified dimmer voltage V_(φ) _(—) _(R). If a rising edgeof the rectified input voltage V_(φ) _(—) _(R) has not been detected,then the dimmer 414 is still phase cutting the supply voltage V_(SUPPLY)and no voltage is available to boost the link voltage V_(LINK). So,operation 502 continues to enable the low impedance path statecontroller 404. An exemplary system and method for detecting a phase cutincluding detecting the leading edges of the rectified dimmer voltageV_(φ) _(—) _(R) is described in U.S. patent application Ser. No.12/858,164, filed on Aug. 17, 2010, entitled Dimmer Output Emulation,inventor John L. Melanson, and assignee Cirrus Logic, Inc., which isreferred to herein as “Melanson I” and incorporated by reference in itsentirety. Another exemplary system and method for detecting the leadingedges of the rectified dimmer voltage V_(φ) _(—) _(R) is described inU.S. patent application Ser. No. 13/077,483, filed on Mar. 31, 2011,entitled Dimmer Detection, inventors Robert T. Grisamore, Firas S.Azrai, Mohit Sood, John L. Melanson, and Eric J. King and assigneeCirrus Logic, Inc., which is referred to herein as Grisamore I and alsoincorporated by reference in its entirety.

If a leading edge of the dimmer voltage V_(φ) _(—) _(R) is detected,then operation 508 disables the low impedance path state controller 404.When the leading edge of the dimmer voltage V_(φ) _(—) _(R) is detected,state A ends and state B begins. At the beginning of state B, operation510 enables the switch mode power conversion controller 406. The switchmode power conversion controller 406 controls switching power converter436 by generating the switch control signal CS to regulate the linkvoltage V_(LINK) as, for example, described in U.S. patent applicationSer. No. 12/496,457, filed on Jun. 30, 2009, entitled Cascode ConfiguredSwitching Using At Least One Low Breakdown Voltage Internal, IntegratedCircuit Switch To Control At Least One High Breakdown Voltage ExternalSwitch, inventor John L. Melanson, and assignee Cirrus Logic, Inc.,which is hereby incorporated by reference in its entirety. When switchmode power conversion controller 406 generates switch control signal CSto cause FET 422 to conduct, the input current i_(R) energizes inductor438 to increase the voltage across inductor 438. When switch mode powerconversion controller 406 generates switch control signal CS to causeFET 422 to stop conducting, the input current i_(R) boosts the voltageacross the link voltage across link capacitor 440. Diode 442 preventscurrent flow from link capacitor 440 into inductor 438 or FET 422.During operation 510, the dimmer current i_(DIM) is approximatelyconstant as indicated, for example, by the dimmer current i_(DIM) at608.

While the switch mode power conversion controller 406 is enabled inoperation 510, operation 512 determines if the energy transferred to theload 308 is greater than an energy transfer parameter ET_(TH) or thedimmer voltage V_(φ) _(—) _(R) is less than a dimmer threshold voltageV_(φ) _(—) _(R) _(—TH) . In at least one embodiment, operation 512determines if the energy transferred from the dimmer 414 is greater thanan energy transfer parameter ET_(TH) by determining an amount of timesince the beginning of state B. If the time exceeds a particularthreshold, then the dimmer 414 has transferred a sufficient amount ofenergy to the power converter system 410. In at least one embodiment,the amount of time is sufficient to allow capacitor 121 (FIG. 1) todischarge so that the dimmer 414 operates consistently from cycle tocycle of dimmer voltage V_(φ) _(—) _(R). An exemplary amount of time is100-300 μsecs. In at least one embodiment, the energy parameter ET_(TH)is a target link voltage V_(LINK) _(—) _(TARGET). In this embodiment,operation 512 determines if the energy transferred from the dimmer 414is greater than an energy transfer parameter ET_(TH) by determining ifthe link voltage V_(LINK) is greater than the target link voltageV_(LINK) _(—) _(TARGET), then the link capacitor 440 has beensufficiently boosted. If the link voltage V_(LINK) is not greater thanthe target link voltage V_(LINK) _(—) _(TARGET), the link voltageV_(LINK) should be further boosted if the dimmer voltage V_(φ) _(—) _(R)is greater than a rectified dimmer threshold voltage V_(φ) _(—) _(R)_(—TH) . In at least one embodiment, if the dimmer voltage V_(φ) _(—)_(R) is less than a dimmer threshold voltage V_(φ) _(—) _(R) _(—TH) ,the dimmer voltage V_(φ) _(—) _(R) is too low to efficiently transferenergy to the load 308 from the voltage supply 412.

Thus, if sufficient energy has not been transferred to the load 308 orthe rectified dimmer voltage V_(φ) _(—) _(R) is greater than therectified dimmer threshold voltage V_(φ) _(—) _(R) _(—TH) , thenoperation 510 continues to enable the switch mode power conversioncontroller 406 and, thus, continues to boost the link voltage V_(LINK).

In operation 512, if sufficient energy has been transferred to the load308 or the rectified dimmer voltage V_(φ) _(—) _(R) is less than therectified dimmer threshold voltage V_(φ) _(—) _(R) _(—TH) , thenoperation 515 causes the switch mode power conversion controller 406 tostop boosting the link voltage V_(LINK), state B ends, state C begins,and operation 516 enables the inactive state controller 408. The“inactive” state controller 408 is not itself inactive. In at least oneembodiment, the inactive state controller 408 causes the dimmer currenti_(DIM) to drop to approximately 0 A and determines zero crossings andleading edges of the dimmer voltage V_(φ) _(—) _(R).

The rectified dimmer current i_(R) is inversely proportional to therectified dimmer voltage V_(φ) _(—) _(R). During state C when theinactive state controller 408 is enabled, the inactive state controller408 controls the flow of the rectified dimmer current i_(R) so that thevoltage at node 444 emulates the actual rectified dimmer voltage V_(φ)_(—) _(R) for a part of the cycle of the rectified dimmer voltage V_(φ)_(—) _(R) that occurs when the link voltage V_(LINK) is less than thetarget link voltage V_(LINK) _(—) _(TARGET) and after a detection of aleading edge of the rectified dimmer voltage V_(φ) _(—) _(R). While theinactive state controller 408 emulates the rectified dimmer voltageV_(φ) _(—) _(R), the inactive state controller 408 effectively isolatesthe power converter system 410 from the dimmer 414, and the emulateddimmer output voltage V_(φ) _(—) _(R) allows the power converter system410 and load 308 to function in a normal mode that is equivalent to whenthe dimmer 414 ideally continues to conduct until the supply voltageV_(SUPPLY) reaches approximately 0V. An exemplary inactive statecontroller 408 is described in conjunction with FIG. 7 and in MelansonI.

Operation 518 determines whether the rectified input voltage V_(φ) _(—)_(R) is at or near the next zero crossing, such as zero crossing 606. Ifthe rectified input voltage V_(φ) _(—) _(R) is not at or near the nextzero crossing, the inactive state controller 408 continues to generatethe emulated dimmer voltage V_(φ) _(—) _(R). If the rectified inputvoltage V_(φ) _(—) _(R) is at or near the next zero crossing, operation520 disables the inactive state controller 408, and controller functioncoordination process 500 returns to operation 502 and repeats.

The enable/disable states 610 depict when the low impedance path statecontroller 404, switch mode power conversion controller 406, andinactive state controller 408 are enabled and disabled. A logical 1indicates enabled, and a logical 0 indicated disabled. Thus, theenable/disable states 608 depict one embodiment of how the controller402 can coordinate the functions of low impedance path state controller404, inactive state controller 408, and switch mode power conversioncontroller 406.

The inactive state controller 408 can be implemented as a digital,analog, or as an analog and digital circuit. FIG. 7 depicts an inactivestate controller 700, which represents one embodiment of inactive statecontroller 408. Inactive state controller 700 functions in part as acurrent source that controls the current i_(R). Inactive statecontroller 700 includes a pull-down circuit 702 to pull-down currenti_(R) after a triac of dimmer 414 turns OFF, and a hold or “glue”circuit 704 to hold the emulated dimmer output voltage V_(φ) _(—) _(R)to approximately 0V until the triac 106 fires in a next half-cycle ofdimmer voltage V_(DIM).

Since, in at least one embodiment, the supply voltage V_(SUPPLY) is acosine wave, and the current i_(R) is directly related to the derivativeof the emulated dimmer output voltage V_(φ) _(—) _(R), an idealrelationship between the current i_(R) and the emulated dimmer outputvoltage V_(φ) _(—) _(R) for a half cycle of supply voltage V_(SUPPLY) isa quarter sine wave. However, a linearly decreasing relationship betweencurrent i_(R) and emulated dimmer output voltage V_(φ) _(—) _(R) is aclose approximation of a quarter sine wave. The current i_(R) versusemulated dimmer output voltage V_(φ) _(—) _(R) causes the powerconverter system 410 to generate an oval emulated dimmer output voltageV_(φ) _(—) _(R), which is a close approximation to a phase cut supplyvoltage V_(SUPPLY).

In general, the pull-down circuit 702 creates the linearly decreasingrelationship between current i_(R) and emulated dimmer output voltageV_(φ) _(—) _(R). The pull-down circuit 702 includes an operationalamplifier 705 which includes a non-inverting input terminal “+” toreceive a pull-down reference voltage V_(REF) _(—) _(PD). A feedbackloop with voltage divider R1 and R2 between the emulated dimmer outputvoltage V_(φ) _(—) _(R) terminal 711 and voltage V_(B) at node 712creates an inverse relationship between voltage V_(B) and emulateddimmer output voltage V_(φ) _(—) _(R). Thus, as the emulated dimmeroutput voltage V_(φ) _(—) _(R) decreases, operational amplifier 705drives the gate of n-channel metal oxide semiconductor field effecttransistor (NMOSFET) 708 to increase the voltage V_(B) so that thevoltage V_(A) at the inverting terminal “−” matches the referencevoltage V_(REF) _(—) _(PD) at the non-inverting terminal “+”. Similarly,as the emulated dimmer output voltage V_(φ) _(—) _(R) increases,operational amplifier 705 drives the gate of n-channel metal oxidesemiconductor field effect transistor (NMOSFET) 708 to decrease thevoltage V_(B) so that the voltage V_(A) at the inverting terminal “−”continues to match the reference voltage V_(REF) _(—) _(PD) at thenon-inverting terminal “+”.

The voltage V_(DRIVE) at the gate of NMOSFET 706 maintains NMOSFET 706in saturation mode. In at least one embodiment, voltage V_(DRIVE) is+12V. The voltage V_(B) across resistor 714 determines the value ofcurrent i_(R), i.e. i_(R)=V_(B)/R3, and “R3” is the resistance value ofresistor 714. Thus, current i_(R) varies directly with voltage V_(B)and, thus, varies inversely with emulated dimmer output voltage V_(φ)_(—) _(R). From the topology of pull-down circuit 702, voltage V_(B) isrelated to the reference voltage V_(REF) _(—) _(PD) in accordance withEquation [Error! Bookmark not defined.]:

$V_{B} = {{V_{{REF}\_{PD}} \cdot \frac{{R\; 1} + {R\; 2}}{R\; 1}} - {\frac{R\;{2 \cdot V_{{\Phi\_}R}}}{R\; 1}\mspace{14mu}\left\lbrack {{{Error}!}\mspace{14mu}{Bookmark}\mspace{14mu}{not}\mspace{14mu}{{defined}.}} \right\rbrack}}$

R1 is the resistance value of resistor 707, and R2 is the resistancevalue of resistor 709. If R1>>R2, then the voltage V_(B) is representedby Equation

[Error! Bookmark not defined.]

$V_{B} \approx {V_{{REF}\_{PD}} - {\frac{R\;{2 \cdot V_{{\Phi\_}R}}}{R\; 1}\mspace{14mu}\left\lbrack {{{Error}!}\mspace{14mu}{Bookmark}\mspace{14mu}{not}\mspace{14mu}{{defined}.}} \right\rbrack}}$

Since i_(R)=V_(B)/R3, if R1 is 10 Mohms, R2 is 42 kohms, and R3 is 1kohm, in accordance with Equation [Error! Bookmark not defined.], i_(R)is represented by Equation [Error! Bookmark not defined.]:

$i_{R} \approx {0.8\left( {1 - \frac{V_{{\Phi\_}R}}{190}} \right)\mspace{14mu}{{mA}\mspace{14mu}\left\lbrack {{{Error}!}\mspace{14mu}{Bookmark}\mspace{14mu}{not}\mspace{14mu}{{defined}.}} \right\rbrack}}$

Once the pull-down circuit 702 lowers the emulated dimmer output voltageV_(φ) _(—) _(R) to a glue down reference voltage V_(REF) _(—) _(GL), theglue-down circuit 704 holds the emulated dimmer output voltage V_(φ)_(—) _(R) at or below a threshold voltage, such as approximately 0V,until the triac 106 fires and raises the emulated dimmer output voltageV_(φ) _(—) _(R). The glue-down reference voltage V_(REF) _(—) _(GL)represents one embodiment of the zero crossing voltage threshold V_(ZC)_(—) _(TH) discussed in conjunction with FIG. 3. Comparator 716 ofglue-down circuit 704 compares the emulated dimmer output voltage V_(φ)_(—) _(R) with the glue-down reference voltage V_(REF) _(—) _(GL). Theparticular value of the glue-down reference voltage V_(REF) _(—) _(GL)is a matter of design choice. In at least one embodiment, voltageV_(REF) _(—) _(GL) is set so that the glue-down circuit 704 holds thevoltage V_(φ) _(—) _(R) to approximately 0V when the voltage V_(φ) _(—)_(R) approaches 0V. In at least one embodiment, the glue-down referencevoltage V_(REF) _(—) _(GL) is set to 5V. Since NMOSFET 706 operates insaturation mode, the voltage at node 710 is approximately equal toemulated dimmer output voltage V_(φ) _(—) _(R). When emulated dimmeroutput voltage V_(φ) _(—) _(R) is greater than the glue-down referencevoltage V_(REF) _(—) _(GL), the output voltage V_(COMP) of comparator716 is a logical 0. In at least one embodiment, the comparator outputvoltage V_(COMP) is passed directly as signal GLUE_ENABLE to a controlterminal of switch 718. Switch 718 can be any type of switch and is, forexample, an NMOSFET. When the comparator output voltage V_(COMP) is alogical 0, switch 718 is OFF, and NMOSFETs 720 and 722 are also OFF. Atransition of the comparator output voltage V_(COMP) from a logical 1 toa logical 0 indicates a determined zero crossing of the dimmer voltageV_(φ) _(—) _(R), which is used by operation 518 of controller functioncoordination process 500 (FIG. 5).

When emulated dimmer output voltage V_(φ) _(—) _(R) transitions fromgreater than to less than the glue-down reference voltage V_(REF) _(—)_(GL), the comparator output voltage V_(COMP) changes from a logical 0to a logical 1. A transition of the comparator output voltage V_(COMP)from a logical 0 to a logical 1 indicates a determined leading edge ofthe dimmer voltage V_(φ) _(—) _(R), which is used by operation 506 ofcontroller function coordination process 500 (FIG. 5). When thecomparator output voltage V_(COMP) is a logical 1, NMOSFETs 720 and 722conduct. NMOSFETs 720 and 722 are configured as a current mirror sharinga common gate terminal 724. A current source 726 generates a gluecurrent i_(GLUE), which is mirrored through NMOSFET 720. In at least oneembodiment, when emulated dimmer output voltage V_(φ) _(—) _(R) is lessthan glue-down reference voltage V_(REF) _(—) _(GL), current i_(R) isapproximately equal to the glue current i_(GLUE). In at least oneembodiment, the glue current i_(GLUE) is set to a value large enough tohold the emulated dimmer output voltage V_(φ) _(—) _(R) at approximately0V until a triac of the dimmer 414 fires again. In at least oneembodiment, the glue current i_(GLUE) is at least as large as a holdingcurrent value HC of dimmer 414 (FIG. 4), such as 250 mA. Thus, the gluecircuit 704 draws a steady state glue current i_(GLUE) from the powerconverter system 410 to maintain the emulated dimmer output voltageV_(φ) _(—) _(R) at or below a threshold voltage, such as approximately0V, during a period of time from when the pull-down circuit 702 lowersthe emulated dimmer output voltage V_(φ) _(—) _(R) to the glue downreference voltage V_(REF) _(—) _(GL) until the triac 106 fires andraises the emulated dimmer output voltage V_(φ) _(—) _(R).

In at least one embodiment, the glue circuit 704 also includespull-down, glue logic (“P-G logic”) 728. The P-G logic 728 generates thesignal GLUE_ENABLE to control conductivity of switch 718. The particularfunction(s) of P-G logic 728 are a matter of design choice. For example,in at least one embodiment, P-G logic 728 enables and disables theglue-down circuit 704. In at least one embodiment, to enable and disablethe glue-down circuit 704, P-G logic 728 determines whether the dimmeroutput voltage V_(φ) _(—) _(DIM) contains any phase cuts as, forexample, described in Grisamore I. If the dimmer output voltage V_(φ)_(—) _(DIM) does not indicate any phase cuts, then the P-G logic 728disables the glue down circuit 704 by generating the GLUE_ENABLE signalso that switch 718 does not conduct regardless of the value ofcomparator output voltage V_(COMP). In at least one embodiment, P-Glogic 728 includes a timer (not shown) that determines how often thecomparator output voltage V_(COMP) changes logical state. If the timebetween logical state changes is consistent with no phase cuts, P-Glogic 728 disables the glue-down circuit 704. Additional, exemplarydiscussion of the inactive state controller 700 is described in MelansonI. The particular system and method of determining a zero crossing ofthe dimmer voltage V_(φ) _(—) _(R) is a matter of design choice. U.S.provisional patent application No. 61/410,269 describes anotherexemplary system and method for determining a zero crossing of thedimmer voltage V_(φ) _(—) _(R). U.S. provisional patent application No.61/410,269, filed on Nov. 4, 2010, entitled “Digital Resynthesis ofInput Signal Dimmer Compatibility”, inventors John L. Melanson and EricJ. King, attorney docket no. 1883-EXL, is hereby incorporated byreference in its entirety.

Thus, an electronic system includes a controller that coordinates thefunctions of a glue circuit, a dimmer emulator, and a switch mode powerconversion controller to provide compatibility between a dimmer and aload.

Although embodiments have been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed is:
 1. An apparatus, wherein a dimmer voltage to a powerconverter system comprises three states that occur from: D. anapproximately zero volt crossing of the dimmer voltage of a dimmer untila phase cut, leading edge of the dimmer voltage; E. an end of state Auntil energy transferred to a load is sufficient to meet at least oneenergy transfer parameter; and F. an end of state B until a beginning ofstate A, the apparatus comprising: a controller configured to: for stateA, enable a low impedance path for a dimmer current of the dimmer,wherein the impedance of the low impedance path is sufficiently low tomaintain a stable phase angle of the dimmer; for state B, enable controlof switch mode power conversion of the dimmer voltage; and control theswitch mode power conversion to maintain the dimmer current above acurrent threshold; and for state C, enter an inactive state, whereinduring the inactive state the low impedance path and the control of modepower conversion is disabled.
 2. The apparatus of claim 1 wherein the atleast one energy transfer parameter comprises a link voltage thresholdvalue, to determine when the energy transferred to a load is sufficientto meet an energy transfer parameter the controller is furtherconfigured to at least: determine when a link voltage is less than thelink voltage threshold value, wherein sufficient energy is transferredto the load when the link voltage is less than the link voltagethreshold value.
 3. The apparatus of claim 1 wherein state B furthercomprises an end of state A until energy transferred to a load issufficient to meet at least a first energy transfer parameter and untilenergy transferred from the dimmer is sufficient to meet at least asecond energy transfer parameter.
 4. The apparatus of claim 1 whereinthe second energy transfer parameter is an amount of time during whichthe dimmer is conducting a supply voltage.
 5. The apparatus of claim 1wherein the controller is further configured to at least: determineoccurrences of the phase cut, leading edge of the dimmer voltage.
 6. Theapparatus of claim 5 wherein the controller is further configured to atleast: disable the low impedance path for the dimmer current when thelink voltage is below the link threshold voltage value and the phasecut, leading edge of the dimmer voltage is determined.
 7. The apparatusof claim 1 wherein the controller is configured to: enable control ofmode power conversion of the dimmer voltage; determine when a linkvoltage of a switching power converter is greater than a link voltagethreshold value; determine when the dimmer voltage is less than a dimmervoltage threshold value; disable switch mode power conversion when thelink voltage is greater than the link voltage threshold value and thedimmer voltage is less than the dimmer voltage threshold value; andenter the inactive state after disablement of the switch mode powerconversion.
 8. The apparatus of claim 1 wherein the controller isconfigured to: enter the inactive state; determine when the dimmervoltage corresponds to the approximately zero volt crossing of thedimmer voltage; and enable the low impedance path for the dimmer currentwhen the dimmer voltage corresponds to the approximately zero crossingof the dimmer voltage.
 9. The apparatus of claim 1 wherein thecontroller is configured to: a. enable the low impedance path for thedimmer current; b. determine when a link voltage is less than a firstlink voltage threshold value; c. determine occurrences of the phase cut,leading edge of the dimmer voltage; d. disable the low impedance pathfor the dimmer current when the link voltage is below the link thresholdvoltage value and the phase cut, leading edge of the dimmer voltage isdetermined; e. enable control of mode power conversion of the dimmervoltage; f. determine when a link voltage of a switching power converteris greater than a link voltage threshold value; g. determine when thedimmer voltage is less than a dimmer voltage threshold value; h. disableswitch mode power conversion when the link voltage is greater than thelink voltage threshold value and the dimmer voltage is less than thedimmer voltage threshold value; i. enter the inactive state afterdisablement of the switch mode power conversion; j. determine when thedimmer voltage corresponds to the approximately zero volt crossing ofthe dimmer voltage; and k. enable the low impedance path for the dimmercurrent when the dimmer voltage corresponds to the approximately zerocrossing of the dimmer voltage.
 10. The apparatus of claim 9 wherein thecontroller is configured to repeat b through k for each cycle of thedimmer voltage, wherein the dimmer voltage is rectified.
 11. Theapparatus of claim 1 wherein the load comprises one or more lightemitting diodes.
 12. The apparatus of claim 1 further comprising aboost-type switching power converter coupled to the controller, whereinthe control of the switch mode power converter comprises control of theboost-type switching power converter.
 13. The apparatus of claim 1:wherein the controller includes a dimmer voltage emulator, and thedimmer output emulator is configured to cause a power converter systemto generate an emulated dimmer voltage, wherein the emulated dimmervoltage emulates part of a cycle of the dimmer voltage.
 14. Theapparatus of claim 1 wherein the dimmer comprises a triode foralternating current (triac).
 15. The apparatus of claim 1 wherein thedimmer voltage is a rectified dimmer voltage.
 16. The apparatus of claim1 wherein the current threshold is sufficient to prevent the dimmer fromprematurely resetting.
 17. A method wherein a dimmer voltage to a powerconverter system comprises three states that occur from: A. anapproximately zero volt crossing of the dimmer voltage of a dimmer untila phase cut, leading edge of the dimmer voltage; B. an end of state Auntil energy transferred to a load is sufficient to meet at least oneenergy transfer parameter; and C. an end of state B until a beginning ofstate A; the method comprising: for state A, enabling a low impedancepath for a dimmer current of the dimmer, wherein the impedance of thelow impedance path is sufficiently low to maintain a stable phase angleof the dimmer; for state B: enabling control of switch mode powerconversion of the dimmer voltage; and controlling switch mode powerconversion to maintain the dimmer current above a threshold; and forstate C, entering an inactive state, wherein during the inactive statethe low impedance path and the control of mode power conversion isdisabled.
 18. The method of claim 17 wherein the at least one energytransfer parameter comprises a link voltage threshold value, the methodfurther comprising: determining when a link voltage is less than thelink voltage threshold value, wherein sufficient energy is transferredto the load when the link voltage is less than the link voltagethreshold value.
 19. The method of claim 17 wherein state B furthercomprises an end of state A until energy transferred to a load issufficient to meet at least a first energy transfer parameter and untilenergy transferred from the dimmer is sufficient to meet at least asecond energy transfer parameter.
 20. The method of claim 17 wherein thesecond energy transfer parameter is an amount of time during which thedimmer is conducting a supply voltage.
 21. The method of claim 17further comprising: determining occurrences of the phase cut, leadingedge of the dimmer voltage.
 22. The method of claim 21 furthercomprising: detecting occurrences of the phase cut, leading edge of thedimmer voltage.
 23. The method of claim 21 further comprising: disablingthe low impedance path for the dimmer current when the link voltage isbelow the link threshold voltage value and the phase cut, leading edgeof the dimmer voltage is determined.
 24. The method of claim 17 furthercomprising: enabling control of mode power conversion of the dimmervoltage; determining when a link voltage of a switching power converteris greater than a link voltage threshold value; determining when thedimmer voltage is less than a dimmer voltage threshold value; disablingswitch mode power conversion when the link voltage is greater than thelink voltage threshold value and the dimmer voltage is less than thedimmer voltage threshold value; and entering the inactive state afterdisabling of the switch mode power conversion.
 25. The method of claim17 further comprising: entering the inactive state; determining when thedimmer voltage corresponds to the approximately zero volt crossing ofthe dimmer voltage; and enabling the low impedance path for the dimmercurrent when the dimmer voltage corresponds to the approximately zerocrossing of the dimmer voltage.
 26. The method of claim 17 furthercomprising: a. enabling the low impedance path for the dimmer current;b. determining when a link voltage is less than a first link voltagethreshold value; c. determining occurrences of the phase cut, leadingedge of the dimmer voltage; d. disabling the low impedance path for thedimmer current when the link voltage is below the link threshold voltagevalue and the phase cut, leading edge of the dimmer voltage isdetermined; e. enabling control of mode power conversion of the dimmervoltage; f. determining when a link voltage of a switching powerconverter is greater than a link voltage threshold value; g. determiningwhen the dimmer voltage is less than a dimmer voltage threshold value;h. disabling switch mode power conversion when the link voltage isgreater than the link voltage threshold value and the dimmer voltage isless than the dimmer voltage threshold value; i. entering the inactivestate after disablement of the switch mode power conversion; j.determining when the dimmer voltage corresponds to the approximatelyzero volt crossing of the dimmer voltage; and k. enabling the lowimpedance path for the dimmer current when the dimmer voltagecorresponds to the approximately zero crossing of the dimmer voltage.27. The method of claim 26 further comprising: repeating b through k foreach cycle of the dimmer voltage, wherein the dimmer voltage isrectified.
 28. The method of claim 17 wherein the load comprises one ormore light emitting diodes.
 29. The method of claim 17 furthercomprising: controlling switch mode power conversion to maintain thedimmer current above a threshold comprises controlling switch mode powerconversion of a boost-type switching power converter.
 30. The method ofclaim 17 further comprising: determining the zero volt crossing of thedimmer voltage by causing a power converter system to generate anemulated dimmer voltage, wherein the emulated dimmer voltage emulatespart of a cycle of the dimmer voltage.
 31. The method of claim 17wherein the dimmer comprises a triode for alternating current (triac).32. The method of claim 17 wherein the dimmer voltage is a rectifieddimmer voltage.
 33. The method of claim 17 wherein the current thresholdis sufficient to prevent the dimmer from prematurely resetting.
 34. Anapparatus wherein a dimmer voltage to a power converter system comprisesthree states that occur from: A. an approximately zero volt crossing ofthe dimmer voltage of a dimmer until a phase cut, leading edge of thedimmer voltage; B. an end of state A until energy transferred to a loadis sufficient to meet at least one energy transfer parameter; and C. anend of state B until a beginning of state A; the apparatus comprising:for state A, means for enabling a low impedance path for a dimmercurrent of the dimmer, wherein the impedance of the low impedance pathis sufficiently low to maintain a stable phase angle of the dimmer; forstate B: means for enabling control of switch mode power conversion ofthe dimmer voltage; and means for controlling switch mode powerconversion to maintain the dimmer current above a threshold; and forstate C, means for entering an inactive state, wherein during theinactive state the low impedance path and the control of mode powerconversion is disabled.